Modulator for high frequency oscillators



M y'4, 1943- E. G. LIQDER 2 31 1 MODULATOR FOR HIGH FREQUENCY OSCILLATORS Origifial FiIed Sept. so, 1938 .Imnentor I Erna-s15 G.Lznder Patented May 4, 194a EJNETE STATES maize arnur FFEQE MODULATOR FOR MGE FREQUENGY SCILLATORS Ernest G. Linder, Philadelphia, Pa, assigncr to Radio Corporation oil-America, a corporation of Delaware Application September 30, 1938, Serial No. 232,661, now Patent No. 2,227,595, dated damn-= ary 7, 1941, which is a division of applicatton Serial No. 36,973, August 2i), 1935, new Patent No. 2,139,238, dated December 6, 1,938. mivided.

and this application June My invention relates to the modulation of high frequency oscillations. More specifically, my invention applies to the modulation of magnetron oscillators.

This application is a division of my copending application Serial No. 232,661, filed September 30, 1938, Patent No. 2,227,595, January '7, 1941, which is in turn a division of U. S. Patent 2,139,238

1, 1940, Serial No.

13 Claims. (c1. 179-1715) to the desired oscillator frequency. Between the center point it and the cathode is an anode bat-= tery it. The negative terminal of i isconnected to the cathode. A pair of modulating coils ll issued to me December 6, 1938, on an application I filed A t 20, 1935.

in United States Patent 2,005,793 which issued on June 25, 1935, to N. E. Lindenblad. The embodiments of my invention, which I am about to describe, are especially suitedto the modulation of magnetrons employing a large inductive winding to develop the permanent magnetic field required for ultra high frequency oscillation. The details of my invention may be best under-. stood by referring to the accompanying drawings and specification.

Figure I represents a magnetron oscillator embodying one form of my invention,

Figures Ha and ED are illustrations of the I electron path in a magnetron oscillator with and without the magnetic field, and

Figure 111 illustrates in schematic form an embodiment of my invention for applying frequency modulation.

In Fig. I, the north and south poles of a magnetic field are represented by N and S; The field may be created with a conventional solenoid with or without an iron core. within the magnetic field is a magnetron l. The cathode 3 lies in a line approximately parallel to the magnetic-flux and 19 are serially connected to battery 2i and microphone 23. The coils it and it are Desitioned so that their magnetic field is substantially in alignment with the field between N and S.

Thecoils may be connected in series or parallel but their fields must be in the same sense. The direction of their fields may eitherv aid or oppose the field between N and S. a

, proposed to use a single magnetic fieldwinding and is energized by a battery 6 or any suitable source of power. Two anodes '1 and 9 are symmetrically arranged about the cathode. The anodes are preferably shaped in the form of a half cylinder. The cathode lies along the central axis of the anodes. The anodes are connected together by a circuit II which may be resonant In'Fig. 11a is a diagrammatic illustration which shows a section of a magnetron oscillator. Within the evacuated envelope 39: is a cathode 33 and the anodes 35 and 31, The radial dotted lines from the cathode to the anodes represent elec tron paths which are not influenced by a mag= netic field. When a magnetic field of proper value, whose flux is substantially parallel to the cathode, is applied, the electron paths become arcuate as shown by the curved dotted lines in Fig. 11b. The cathode heating circuits, anodecircuits, andshatteries are omitted from Figures Ha and 11b for simplicity of illustration.

'Briefly, the efiect of electron flow in a magnetron under the influence of the magnetic field of proper intensity is to set up high frequency oscillations. The wave length of the oscillations may be determined by the equation:

1 A qu 132100 where,

A equals wave length in centimeters Hequals magnetic field in gauss.

An inspection of the equation shows that an increase in H decreases the wave length or increases the frequency. A decrease in H increases the wave length or decreases the frequency. If the normal. steady magnetic field between N and S is varied, the radio oscillations created will be frequency modulated in accordance with the currents altering the magnetic field. Ithas been and vary the magnetizing current flowing therein. While this method may be used in some cases, it is not. suited to frequency modulate an 'ultra high frequency magnetron oscillator. I have found that by employingseparate modulating coils. such as I! and I9, frequency modulation may be employed in "cases where it would be impractical to modulate at voice frequencies when a single large inductive electromagnetic located at an angular position.

employed to generate the normal oscillations and the modulated oscillations.

Although the separate modulating coils may be positioned so that their magnetic fields are substantially parallel to the main magnetic field, I find cases where the modulating fields may be Such an arrangement is shown in Fig. III. In this figure the coil or, coils are arranged so that the flux generated bycurrents flowing in the modulating coil is at a right angle to the flux of the main magnetron field. In showing a right angle, I do not intend to be limited to precisely 90 because other angular arrangements may be used. The angular relationship is a decided advantage in that the action of the modulating coils is not greatly affected by the usual large iron core of the main magnet as is the case in the arrangement of Fig. I. The resulting flux is the vectoral sum of the modulating coil flux and the main 'magnetron coil flux. The combined fluxes produce frequency modulated oscillations.

It is often desirable to frequency modulate without any variations in the amplitude of the oscillatory currents. In the preceding description, the frequency modulation is accompanied by some amplitude modulation. The undesired amplitude modulation may be compensated by the arrangement shown in Fig. III.

In Fig. III a magnetron 4| has within its evacuated envelope, which may be of any suitable shape, two anodes 43 and 45 and cathode 41. The anodes are connected to a resonant circuit 49, which is coupled to the antenna mid-point of the bridging conductor 48 is connected through the secondary 53, of transformer 52 and anode battery 55, to cathode 41. The negative pole of the battery 55 is-connected to cathode. A tertiary winding 51 of transformer 52 is connected to potentiometer 59. Between the lower end of 59 and the slider BI is connected an impedance 6 3. The mid-point of 63 is connected to one terminal of modulating coil 65. The other terminal of 65 is connected to the junction of resistance 61 and capacity 69. The resistance 6'! connects to one end of B3 and the capacity 69 to the-other. The elements 63 61-69 form a phase adjusting circuit. The primary II of transformer 52 is serially connected to battery 13 and microphone 15. It should be understood that any variable signal representing current may be impressed on H, or any of the several modulating circuits. The main magnetic field is represented by the field coil 42 and battery 44.

The current fluctuations in H induce changing potentials in- 51. The varyingpotentials in 5T cause modulating currents to flow in the modulating coil 65. These current changes are accompanied by magnetic flux changes which frequency and amplitude modulate the oscillations produced The The circuit shown in Fig. IIIis the preferred arrangement for frequency modulation. The same circuit may be adjusted for amplitude modulation with the frequency modulation efi'ects cancelling each other.

The foregoing description illustrates one. embodiment of my invention which may be employed to amplitude or frequency modulate a magnetron oscillation. Other modifications within the scope of my invention will occur to those skilled in the art. I' do not intend to limit my invention to the precise arrangement shown except as required by the prior art and the appended claims.

I claim as my invention:

l. The method of modulating a magnetron oscillator having cathode and anode electrodes, means for producing a main magnetic field, and independent means for producing an auxiliary magnetic field at an angle to said main field, which comprises varying the intensity of said auxiliary field in accordance with variations in the amplitude of signal representing currents without varying said main magnetic field, apply-- ing voltages between the electrodes of said magnetron which vary in amplitude in accordance with variations of said signal representing currents, and adjusting the relative phase and intensity of the variations of said auxiliary field and said applied voltages so that said oscillation is modulated in a desired mode in response to said signal representing currents, and the modulation of oscillation in an undesired mode is minimized.

2. A modulated oscillator comprising a magnetron having cathode and anode electrodes, means for producing a fixed magnetic field which surrounds and is substantially parallel to said cathode, separate means for producing a variable magnetic field at an angle to said fixed field whereby variations in said variable field have substantially no effect on said fixed field, means for varying said variable field in accordance with modulating signals to produce a desired andan undesired mode of modulation, and means including said anode and cathode electrodes for reducing said undesired form of modulation.

3. A device ofthe character described in claim 2 in which said desired mode of modulation produces a variation in the frequency of oscillation of said oscillator.

- 2 ,in which said desired mode of modulation prowhich applied to 43 and 45 primarily cause amduces a variation in the amplitude of oscillation of said oscillator.

5. A modulation system for a magnetron oscillator having a. linear cathode and a concentric cylindrical anode comprising means for producing a fixed magnetic field which surrounds and is substantially parallel to said cathode, separate means. for producing a variable magnetic field which surrounds said cathode and is at an angle tosaid fixed field, said magnetic field producing means having substantially no common flux path other than that within the tube itself so that variations in said variable field have substantially no effect on the strength of said fixedlfi'eld, means for varying said variable field in accordance with modulating signals to produce a desired and an undesired mode of modulation, and means including said anode and cathode electrodes for ing signals to modulate said oscillator, meansfor producing a fixed magnetic field which surrounds and is substantially parallel to said cathode, separate means for producing a variable magnetic field which surrounds said cathode and is at an angle to said fixed field, said magnetic field producing means having substantially no common flux path outside of said anode-cathode region so that variations in said variable field havesubstantially no efiect on the strength of said fixed field, means for varying said variable field in accordance with said modulating signals to produce a desired and an undesired mode of modulation, and means for adjusting the relative phase and amplitude of modulations produced by the variation of said potential difference and said variable field to minimize said undesired mode of modulation.

of force substantially parallel to the axis of said cathode, subjecting said stream also to the influence of a modulated fmagnetic field having lines of force lying at an angle to the axis of said cathode, and producing said modulated magnetic field by a current which is simultaneously applied between said cathode and said '7. A modulated oscillator comprising a mag- I netron having cathode and anode electrodes,

means for producing a fixed magnetic fieldwhich surrounds and is substantially parallel to said cathode, separate means for producing a second magnetic field which surrounds said cathode and lies at an angle to said fixed field, means for applying an energizing potential between said cathode and anode electrodes, means for modulating said potential to produce a desired and an undesired mode of modulation in said magnetron, and means for simultaneously modulating said second magnetic field so as to oppose said undesired mode of modulation.

8. A modulated oscillator comprising a magnetron having cathode and anode electrodes,

means for producing a fixed magnetic field which surrounds and is substantially parallel to said cathode, separate means for producing a second magnetic field which surrounds said cathode and lies at an angle to said fixed field, means for applying an energizing potential between said cathode and anode electrodes, means for modulating said potential to produce a desired and an undesired mode of modulation in said magnetron, separate means for modulating said second magnetic field, and means for controlling the relative phase and amplitude of the resultant desired modulations.

9. In a magnetron oscillator having cathode and anode electrodes, means for producing a magnetic field substantially parallel to and sur rounding said cathode, and means producing an auxiliary magnetic field surrounding and lying,

at an angle to said cathode, the method of operation which compri'sesapplying an energizing potential between said cathode and anode electrodes, modulating said energizing potential and said auxiliary field, and controlling the relative amplitude and phase of said modulations.

10. The method of -modulating the output energy of an electron discharge tube of the magnetron type wherein the normal flow of electrons is from a linear cathode outwardly in planes perpendicular to the axis of said cathode toward first one and then another of a plurality of cylindrically-segmented anodes, which comprises subjecting the electron stream of said tube to the influence of a steady magnetic field having lines anodes.

l1. A modulation system for a magnetron discharge tube having a linear cathode and a plus rality of surrounding cylindrically segmented anodes, which comprises means for producing a steady magnetic field substantially parallel to the axis of said cathode and of such strength as to cause electrons to barely graze the inner surfaces of said anodes, means including a modulating source of energy and a magnetic coil energized by said source for deflecting said magnetic field away from parallelism with respect to said cathode axis, means for mounting said coil with such orientation that the deflection component of said magnetic field is a function of the energy variations of said modulating source, and means under control of said modulating source for continuously adjusting the voltage applied between the cathode and the anodes to a value such as to 4 maintain constant the oscillation frequency of said tube. I

12. A modulation system for a magnetron discharge tube having a linear cathode and a plurality of surrounding cylindrically segmented anodes. which comprises means -for producing for causing the amplitude of electronic emission in said tubeto be controlled by said modulating source, without influencing the frequency of oscillations in said tube.

13. A magnetron oscillator system in combination with a modulation source, said system comprising an electron discharge tube having a cylindrical arrangement of "anode segments and a linearcathode centrally disposed within said arrangement, a primary magnetic field producing means for directing lines of force through said tube in adirection-substantially coaxial with respect to said cathode, a secondary field producing means under control of said modulatingsource for deflecting said lines of force angularly with respect to said cathode axis, a cathode-to-anode circuit having a direct current potential source, means including an impedance interconnecting said anode segments for producing oscillations in said tube, said impedance being symmetrically disposed in said cathode-to-anode circuit, and means controlled by said modulations source for continually adjusting the cathode-to-anode p0! tential to a .value such that the frequency of oscillations is maintained substantially constant.

' ERNEST G. LINDER. 

